Human blood vessels occasionally become occluded by clots, plaque, thrombi, emboli or other substances that reduce the blood carrying capacity of the vessel. Cells that rely on blood passing through the occluded vessel for nourishment may die if the vessel remains occluded. This often results in grave consequences for a patient, particularly in the case of cells such as brain cells or heart cells.
Accordingly, several techniques are being developed for removing an occlusion from a blood vessel. Examples of such techniques include the introduction into the vasculature of therapeutic compounds—including enzymes—that dissolve blood clots. When such therapeutic compounds are introduced into the bloodstream, often systematic effects result, rather than local effects. Accordingly, recently catheters have been used to introduce therapeutic compounds at or near the occlusion. Mechanical techniques have also been used to remove an occlusion from a blood vessel. For example, ultrasonic catheters have been developed that include an ultrasound radiating member that is positioned in or near the occlusion. Ultrasonic energy is then used to ablate the occlusion. Other examples of mechanical devices include “clot grabbers” are “clot capture devices”, as disclosed in U.S. Pat. Nos. 5,895,398 and 6,652,536, which are used to withdraw a blockage into a catheter. Other techniques involve the use of lasers and mechanical thrombectomy and/or clot macerator devices.
One particularly effective apparatus and method for removing an occlusion uses the combination of ultrasonic energy and a therapeutic compounds that removes an occlusion. Using such systems, a blockage is removed by advancing an ultrasound catheter through the patient's vasculature to deliver therapeutic compounds containing dissolution compounds directly to the blockage site. To enhance the therapeutic effects of the therapeutic compound, ultrasonic energy is emitted into the dissolution compound and/or the surrounding tissue. See, for example, U.S. Pat. No. 6,001,069.